1. Field of the Invention
The present invention relates to a tread thickness measuring method and, in particular, to a method of measuring the tread thickness from the belt surface located in a radially outer position within a tire to the tread surface.
2. Description of the Related Art
In a conventional method of retreading a used tire, a worn tread of the tire is abraded by buffing into a predetermined shape to form a bonding surface to which a new tread is bonded. Then, through certain steps, the new tread is bonded to the bonding surface. To form the bonding surface, the thickness of tread to be removed must be determined first. So a measurement is taken of the tread thickness from the tread surface to the outermost belt located in the radially outermost position of the belt layer, which is one of the structural members of a tire. The measurement of the tread thickness is done with a non-contact eddy-current sensor, for instance. The eddy-current sensor has a detection coil therein. When a magnetic flux is induced with a high-frequency current passed through the detection coil, an eddy current is created in the belt layer by the induced magnetic flux. This will cause a change in the magnetic flux in the detection coil. And by detecting the change in impedance occurring in the detection coil, the thickness from the tread surface to the outermost belt surface can be measured.